This invention generally relates to a hand-held electromechanical fastener driving tool, and more particularly to a fastener driving tool having an inertial member for imparting kinetic energy to drive a fastener into a workpiece.
In the past, where relatively large energy impulses have been required to operate a fastener driving tool, such as an industrial nailer or stapler, it has been common practice to power such tool pneumatically. Such tools are capable of driving a 3xe2x80x3 or longer nail, or staple, into framing wood such as 2xc3x974s, for example. However, pneumatic driving tools require an on-site air compressor, which is often unavailable or not desired. Also, dragging the pneumatic umbilical is often an impediment to the user.
Corded AC electrical fastener driving tools are often used instead of pneumatic power since electrical power is more often available than air compressors. In particular, much effort has been expended in the prior art in providing heavy duty, high powered, fastener driving tools employing a flywheel as a means of delivering kinetic energy sufficient to drive a heavy duty fasteners. Examples of such systems are disclosed in U.S. Pat. Nos. 4,042,036; 4,121,745; 4,204,622; 4,298,072; and 5,511,715. Use of a flywheel is an attempt to limit the large current draws to actuate a solenoid to drive a fastener. A DC motor is activated over a non-instantaneous period and then the kinetic energy thus developed in the flywheel is clutched to the driver in an xe2x80x9cenergy dumpxe2x80x9d.
While such corded electrical fastener driving tools may perform well, in many instances an AC outlet is not available. Even if an AC outlet is available, many users find dragging the electrical cord to be an impediment to use. To address these preferences, it is further known to employ a portable power source such as a battery, such as solenoid-operated fastener driving tools. These portable fastener driving tools are primarily used in light-duty applications such as in driving one inch brad nails, for example, rather than the larger 2xe2x80x3 to 4xe2x80x3 staples or nails used in framing. In particular, the large amount of peak power required limits applications to small fasteners since the batteries inefficiently provide power during peak electrical current demands, with the internal resistance of the battery generating heat in response. The build up of heat also tends to degrade the service life of the battery. In addition, the large influxes of current limit the types of batteries suitable for this application, such as being limited to Nickel Cadmium batteries.
The corded electrical flywheel operated hand tools are generally unsuitable for use of a battery due to their power consumption. Although use of a flywheel reduces the current surges, the generally known corded flywheel operated hand tools accelerate the flywheel often to a speed greater than required so that enough speed is generated at lower battery charge conditions. In addition, the clutching performance used may also vary due to the amount of manufacturing tolerance variation and wear. Consequently, these tools generally bring the flywheel to a stop during each drive cycle, even if a large portion of the kinetic energy of the flywheel is wasted thereby. Thus, over-accelerating the flywheel and exhausting all of the kinetic energy each cycle rapidly would exhaust a battery.
One approach to an efficient portable electrically driven tool is a multiple impact tool, such as described in U.S. Pat. No. 4,625,903, wherein a linear inertial member is repeatedly raised by a cam against a compression spring and released to impact a fastener. An electrical motor and portable battery pack are operated in a more efficient manner by running the motor for a period of time rather than providing a surge of power to a device such as a solenoid. The relatively small amount of energy stored in the spring each cycle typically requires a large number of impacts to drive a staple or nail into a workpiece. However, while the multiple impact tool is efficient and effective in driving fasteners, some users prefer a single driving action comparable to pyrotechnic or compressed air systems. The multiple impact tools also can damage a wood surface due to the vibrations the tool generates while stroking.
Therefore, a significant need exists for a portable fastener driving tool that drives a fastener into a workpiece with a single driving action, yet has the advantages of being portable. It would be further desired to have such a tool that could drive large fasteners.
These and other problems in the prior art are addressed by a control system for controlling use of a flywheel in imparting kinetic energy to drive a fastener such as a staple or nail into a workpiece. A control system for a battery-powered fastener-driving tool provides safe and efficient operation for a range of fastener types and for a wide range of operating conditions. In particular, the control system advantageously adapts to battery power conditions and the performance of components of the tool by sensing and being responsive to the amount of kinetic energy stored in an inertial driving member, such as a flywheel. In addition, the control system provides advantages of compensating for manufacturing tolerance variation or wear in the clutching of the flywheel yet does not waste kinetic energy nor over-drive a fastener.
In one aspect of the invention, a method is given for driving a fastener into a workpiece with kinetic energy from an electrically accelerated flywheel. In particular, selective actuation of a clutch assembly to impart the kinetic energy to a driver to the fastener is in response to sensing a parameter of the flywheel indicative of kinetic energy thereof. Thereby, the kinetic energy may be developed over a period of time efficient for portable electric devices such as batteries, yet still provide a large impulse of kinetic energy to drive the fastener in a single drive.
In another aspect of the invention, a portable hand tool has an inertial member that is accelerated by a motive device. The inertial member is selectively coupled by a clutch to a driver to impart kinetic energy to a fastener for driving the fastener into a workpiece. A controller includes a sensor that senses a parameter of the inertial member indicative of kinetic energy therein. The controller also includes a circuit arrangement that commands the clutch to impart the kinetic energy of the inertial member in response the sensed parameter and a target value. Including a sensor provides advantages of more accurately measuring the amount of kinetic energy to be imparted to the fastener. The ability to consistently and adaptively provide a given amount of driving force to a fastener extends the portability of a hand tool by allowing use of batteries rather than having to be corded or to use another source of power (e.g., pneumatic, pyrotechnic).
These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.